In prior-art central buffer couplings, the coupling head projects beyond the vehicle profile on the front side. Central buffer couplings, whose coupling head can be pivoted into the vehicle profile when not in use, can be considered for use especially for rail-borne vehicles which do not travel on lines of their own, e.g., streetcars, in order to avoid a hazard for other road users due to a coupling head projecting beyond the railborne vehicle on the front side.
U.S. Pat. No. 4,049,129 discloses a central buffer coupling of the type described in the introduction, in which the fixing device has a vertical locking pin, which is fastened to the rear shaft part, passes through an arc-shaped, slot-like opening provided on the front shaft part and is concentric with the axis of the connecting pin, and on which a locking ring having an outer cone is axially displaceable by means of an adjusting device, which can be operated manually.
At its two ends, the slot-like opening has a conical locking depression each, and the locking ring can be pushed by means of the adjusting device into one of the locking depressions in the extended position of the two shaft parts, and into the other locking depression in the mutually pivoted position of the shaft parts.
To release the fixing device, the locking ring can be lifted out of the locking depression in question by the adjusting device.
The fixing device has a complicated design in this prior-art embodiment, because not only are the locking pin, the slot-like opening with the locking depressions, as well as the locking ring necessary, but the adjusting device for the locking ring must also be made of a plurality of individual parts, because it must bring about the axial displacement of the locking ring on the locking pin, on the one hand, and, on the other hand, it must secure the locking ring in its position corresponding to the mutually extended position of the two shaft parts.
DE 32,13,697 A1 discloses a central buffer coupling, in which a sliding sleeve, which is mounted on the coupling shaft in such a way that it is able to be displaced to a limited extent in the longitudinal direction of the coupling shaft, is provided as the fixing device, and the said sliding sleeve is displaceable, by the force of the springs, in the mutually extended position of the two shaft parts, into a locked position, in which the sliding sleeve overlaps both shaft parts to make the coupling shaft rigid, and a cam, connected nonrotatably to the connecting pin, is arranged at each end of the connecting pin, and the said cam has a cam surface, which is eccentric with the axis of the connecting pin and cooperates with the front surface of the sliding sleeve facing it, and the said cams form a stop for the sliding sleeve in their locked position, and by pivoting the cams, the sliding sleeve can be displaced against the force of the springs into an unlocked position, which makes it possible to pivot the front shaft part, and in which the sliding sleeve can be fixed.